By Prof. Bob Andoh

Current estimates of the costs required to address combined sewer overflow (CSO) problems are in the $50 billion range and rising. The majority of the cost is made up of chambers and other equipment required to separate solids and disinfect the much higher volume of stormwater-sewage mix that is generated during heavy rains. These estimated costs are based on the use of conventional technology, which requires relatively large sedimentation and contact tanks in order to achieve the level of solids separation or disinfection needed to meet applicable environmental regulations.

Hydrodynamic vortex separators (HDVSs) have been identified as a possible means of reducing the capital expenditures required to address CSOs. A key advantage is that a single HDVS is capable of both solids separation and disinfection, providing a significant reduction in the capital expenditures required to handle CSOs. Another advantage is that the flow properties of a single HDVS can be optimized to greatly improve the efficiency of both solids separation and contact disinfection compared to conventional technology. This means that HDVSs can handle the same CSO volume as conventional contact tanks that are 5 times larger. The resulting reduction in tank size and construction costs typically reduces overall project costs by about 50%.

By David Mongeau

Stormwater equipment manufacturers spend most of their waking moments trying to outmaneuver each other in business. While

By Robert Y.G. Andoh, Mike Faram and Dave Scott

Water industry officials throughout Europe – and in a growing number of municipalities in North America – tend to think of vortex valves as a novel technology for outlet flow control on a stormwater detention system. Most of these 17,000+ valves installed around the world are, in fact, implemented on stormwater detention schemes because use of a valve can reduce the required storage volume by up to 50% while still meeting the maximum discharge requirement. But vortex valves actually have many other uses in stormwater, wastewater and combined sewer systems. These versatile devices tackle a number of other problems, including erosion control, re-oxygenation of water and flow equalization in wastewater treatment plants.

By Prof. Bob Andoh

By Robert Y.G. Andoh

Throughout the world, thousands of stormwater pollutant removal systems are being installed in an effort to prevent watercourses from being polluted. As supply has risen to meet demand, a variety of proprietary, chamber-based systems have emerged, including hydrodynamic separators, which are designed to settle out and store sediments and associated pollutants, preventing them from being discharged to the natural environment.

However, recent research suggests that some systems may not be as effective as might be claimed. Some systems are subject to “washout” or “scour,” whereby captured and stored pollutants are flushed from a system during extreme wet weather.